This invention relates to a precision angular displacement mechanism that carries out tracking for an optical record and playback apparatus using a separate optical system and the method of assembling that mechanism.
As shown in FIG. 22, in order to increase the access speed of the optical record and playback apparatus of the prior art, it is common to divide the optical system into a shifting optical system 2 that moves in the radial direction of an optical disk 1 and a stationary optical system (not illustrated) that has a light source. Here, shifting optical system 2 is composed of an object lens 3 and a mirror 4. The stationary optical system is composed of a light source and an angular displacement mechanism called a galvanomirror which does not move in relation to optical disk 1.
The galvanomirror has a reflecting mirror 6 which reflects a laser light 5 emitted from the light source in a direction A to a direction B and minutely displaces reflecting mirror 6 around a direction E. The galvanomirror also has a mechanism that tilts laser light 5 a minute angle (.theta..degree.) in direction B. As a result, laser light 5 is reflected in direction B at reflecting mirror 6. Laser light 5 is then reflected in a direction D at a mirror 4 of shifting optical system 2 and is guided to object lens 3. In addition, reflecting mirror 6 is minutely displaced in direction E. By tilting laser light 5 at a minute angle in direction B, a light spot 8 is always placed on a track 7 on optical disk 1 for tracking purposes.
An example of the galvanomirror of the prior art appears in FIGS. 23 through 26. As shown in these drawings, coils 10a and 10b, which have elliptical windings, are each attached to one side of a holder 9 having a concave cross section shape. A triangular column-shaped reflecting mirror 6 is attached to the cut-out portion of the tapered part of holder 9 by an adhesive. The tip of a holder support component 11, which is made of resin or synthetic rubber and supports holder 9, is an insert molded on the inner side of holder 9. The base end of holder support component 11 is attached to a support unit 12. In the middle of holder support component 11 is a thin hinge 11a that can change its shape elastically.
On the two sides of holder 9 is a magnetic circuit which is composed of magnets 13a and 13b and yokes 14a and 14b. There is an air gap between the magnetic circuit and coils 10a and 10b. Magnets 13a and 13b run along the longitudinal direction of coils 10a and 10b. As shown in FIG. 26, the direction of all magnification is in the same direction. As a result, the magnetic field generated by magnets 13a and 13b interlinks with coils 10a and 10b. In FIG. 26, the direction of that magnetic field is to the right. Because coils 10a and 10b are connected, the current flows in the opposite direction. When current flows through coils 10a and 10b, it follows the Fleming left hand rule. As shown in FIG. 26, a magnetic force is generated in each of coils 10a and 10b. The magnetic forces are in the opposite directions to each other.
As a result, when current flows through coils 10a and 10b, the magnetic force that acts in the opposite direction in coils 10a and 10b functions as the moment that moves the moving section, which is composed of reflecting mirror 6, holder 9 and coils 10a and 10b, around thin hinge 11a. By adjusting the direction and magnitude of the moment, it is possible to make minute adjustments to reflecting mirror 6 to adjust the direction in which the laser light will be reflected relative to shifting optical system 2.
However, in the galvanomirror described above, because thin hinge 11a of holder support component 11 is made of resin or synthetic rubber, the rate of elasticity changes with temperature. As a result, the resonant frequency fluctuates, reducing the control characteristics of reflecting mirror 6. In particular, when coils 10a and 10b are heated up due to continuous current flow, heat is conducted to holder support component 11, the elasticity coefficient of thin hinge 11a decreases and the resonant frequency fluctuates.
In the galvanomirror described above, because the moving section can be rotated by changing elasticity of thin hinge 11a, repetitive stress acts on thin hinge 11a. In particular, at low temperatures, fatigue breakdown occurs. Further, thin hinge 11a, which is made of resin or synthetic rubber, is commonly manufactured by means of injection molding. Therefore, there are variations in the elasticity coefficient of the thin hinge section due to variations in its dimensions caused by variations in the molding conditions and the wear to the mold caused over time, etc. As a result, strict manufacturing control is required.
Moreover, in the galvanomirror described above, under a condition in which no current flows through coils 10a and 10b, the moving section, which includes reflecting mirror 6, should be at its center position. In fact, however, an offset is generated and the moving section tilts toward one side or the other. As a result, the relative positions of coils 10a and 10b and magnets 13a and 13b are also offset. This results in reflecting mirror 6 not being able to achieve its designated angular displacement when the current is flowing through the coils 10a and 10b. Light spot 8 on track 7 of optical disk 1 gets into an offset condition in which it is not accurately positioned on track 7. The cause of the galvanomirror offset is due to the moving section being freely supported by support component 11 of the holder or by the creeping of thin hinge 11a. However, the greatest cause is due to a major fluctuation in the elasticity coefficient of thin hinge 11a due to its temperature characteristics.
Furthermore, as shown in FIG. 26, in the galvanomirror described above, the magnetic field generated by the magnetic circuitry, which is composed of magnets 13a and 13b and yokes 14a and 14b, only interlinks to one of the two effective portions of coils 10a and 10b. This creates problems of poor moment generation efficiency and poor balance. In other words, on coils 10a and 10b, which have elliptical windings, the effective portions are the two upper and lower linear portions that run in the longitudinal direction. However, magnets 13a and 13b correspond to only one of these coils. Therefore, these magnetic fields do not interlink to the other linear section. As a result, because the electromagnetic force that is generated in the effective portions of magnets 13a and 13b and interlinks coils 10a and 10b is not symmetrical to thin hinge 11a, which is at the rotation center of the moving section, the force not only functions as the moment centering on thin hinge 11a, but also acts as a force that causes translational motion.
This invention solves the above problems. By forming the holder support component of a flat metal spring, and by using the elastic deformation of the the flat metal spring to support the holder, to which the reflecting mirror is attached, the fluctuations in the elasticity coefficient of the holder support component caused by the ambient temperature can be controlled. Further, holder support component with a high fatigue strength can be offered. At the same time, the objective of this invention is to offer a method of assembling the holder and the flat metal spring by combining the synthetic resin with the flat metal spring as a single unit using insert molding.
Other objectives of this invention are to increase the generation efficiency of the magnetic force that is generated in the coils, to improve the balance of the force that moves the moving section, to reduce the force that contributes to the translational motion of the moving section, and to offer an optical record and playback apparatus that improves the performance of rotational motion.